Conventionally, networks utilize a variety of transmission media such as optical fiber, copper, coaxial cable, radio frequency (RF), and the like. Additionally, networks are typically architected with a variety of tiers, such as, for example, copper or coax to a home user, wireless to a mobile user, optical or RF to business, optical for long haul and metro service provider connections, and the like. OTN (Optical Transport Network) is an exemplary encapsulation protocol defined for optical transmission for transparently multiplexing and mapping synchronous and asynchronous client signals.
ITU-T defines OTN as a set of Optical Network Elements connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals. ITU Standard G.709 is commonly called Optical Transport Network (OTN) or digital wrapper technology. OTN is currently offered in three rates, OTU1, OTU2, and OTU3, and future rates are expected such as OTU4. OTU1 has a line rate of approximately 2.7 Gb/s and was designed to transport a SONET OC-48 or an SDH STM-16 signal. OTU2 has a line rate of approximately 10.7 Gb/s and was designed to transport an OC-192, STM-64 or 10 Gbit/s WAN. OTU2 can be overclocked (non-standard) to carry signals faster than STM-64/OC-192 (9.953 Gb/s) like 10 gigabit Ethernet LAN PHY coming from IP/Ethernet switches and routers at a full line rate (approximately 10.3 Gb/s). This is specified in G.Sup43 and called OTU2e. OTU3 has line rate of approximately 43 Gb/s and was designed to transport an OC-768 or STM-256 signal. OTU4 is currently under development to transport future 100 GbE signal.
Of note, OTN is defined in various standards such as: ITU-T G.709 Interfaces for the optical transport network (OTN); ITU-T G.798 Characteristics of optical transport network hierarchy equipment functional blocks; OTN Standard FEC (Called GFEC sometimes) is defined in ITU-T G.975; OTN Jitter is defined in ITU-T G.8251: The control of jitter and wander within the optical transport network (OTN); G.870: Terms and definitions for Optical Transport Networks (OTN); G.871: Framework for optical transport network Recommendations; G.873.1: Optical Transport Network (OTN): Linear protection; G.874: Management aspects of the optical transport network element; G.874.1: Optical transport network (OTN): Protocol-neutral management information model for the network element view; G.959.1: Optical transport network physical layer interfaces; G.8201: Error performance parameters and objectives for multi-operator international paths within the Optical Transport Network (OTN). In addition to the OTN Standard FEC (GFEC), a proprietary FEC could be used.
As networks evolve, capacity is always a foremost concern. This is typically the case at all the tiers in a network. For example, copper is bandwidth limited (typically to below 30 Mb/s), fiber is not in place everywhere and is often very expensive to put in place (e.g., $40 k to $80 k per mile for urban deployment), and currently deployed radio is limited to 10 to 45 Mb/s typically (or less), particularly at the access tier (first hop). Note, one advantage of radio is that radio does not require wiring (i.e., copper, fiber, etc.).
Many current networks are radio based, usually in the 6-38 GHz range. This frequency range is referred to as “microwave” links. Spectrum widths available in this range are usually 5 to 50 MHz, thus limiting data rates even with 256 QAM (Quadrature amplitude modulation) coding. Frequencies below 6 GHz are normally used for access, e.g., from consumer handset terminals to a cell tower. The 6-38 GHz radio links are normally point-to-point for backhaul, as multipoint is normally used for consumer handset access and is exceedingly expensive and complex to license. Today, these 6-38 GHz networks are typically sub 45 Mb/s rate especially for access/metro, with metro rates up to 155 Mb/s and transport rates in the Mb/s range, typically.
However with increasing data rates of access terminals, current deployments need to target access around 45 Mb/s, hence access aggregation requires 150 Mb/s to 1,000 Mb/s and metro scaling to n×400 Mb/s to p×Gb/s (n, p are integers). Higher radio frequency bands are becoming open to deployment, such as the “e-band” frequency band which is typically 71-95 GHz (for example 71 to 86 GHz). This band is called millimeter (mm) wave (i.e., as opposed to microwave). Due to propagation characteristics (oxygen absorption) and licensing, the 70-86 GHz range is more suitable to carrier needs than the 60 GHz area (which is thus used for short unlicensed drops to enterprises, usually). Spectrum widths available (currently licensed) at 70-86 GHz are around 2*5 GHz in width. There are also other bands (such as 40-55 GHz).
As described herein, historically radios were plesiochronous (T1, E1, etc.) or SONET/SDH. Also, network bandwidth and services are shifting away from plesiochronous and SONET/SDH to Ethernet, i.e. Ethernet is becoming the service of choice in network deployments. Thus existing radios are not very well suited to carrying Ethernet, although they can be made to carry Ethernet (e.g., Ethernet over SONET/SDH, for example, using a SONET/SDH radio). What has yet to be investigated is the application of OTN transport over radio frequency links for providing Ethernet transport as well as other services used with OTN.